pgsql: Fix inconsistent comments for some function declarations in head

Fix inconsistent comments for some function declarations in headers

Some of the headers list a couple of function prototypes located in a
different file than what is referred to.  This fixes a couple of
places where this inconsistency exists.

Author: Richard Guo
Discussion: https://postgr.es/m/CAMbWs4__RdcSNXPa7L62Ozvo_Q4LvT60o3Bnp8yrQ_m9y5CKvg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/245e14e28b298e6ed00ea8d8c607b62387c9da92

Modified Files
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src/include/access/nbtxlog.h          |  8 ++++++--
src/include/replication/walreceiver.h |  2 +-
src/include/storage/bufmgr.h          | 11 +++++++----
3 files changed, 14 insertions(+), 7 deletions(-)